Within the art of cutting machining, it has become more and more common to use connecting surfaces of the type that are formed with co-operating male- and female-like engagement portions. Particularly frequently, such connecting surfaces are found in the interface between the basic body of the tool and the replaceable cutting insert or inserts. An earlier, simple type of connecting surface—which by those skilled in the art commonly is denominated “serrations”—is built up by a plurality of conformal, straight and parallel ridges of generally V-like cross-section shape, which are spaced apart by grooves having the same general cross-section shape as the ridges. Therefore, the ridges in one of the two connecting surfaces can engage and be wedged up in the grooves in the other connecting surface, and vice versa.
Connecting surfaces of this type counteract relative motions between the components of the tool in one direction, i.e., perpendicular to the ridges. However, relative motions in the direction parallel to the ridges are not prevented. To overcome this imperfection, recently, connecting surfaces have been developed that include not only a certain a number of parallel, longitudinal ridges or male-like engagement portions, but also one or more transverse ridges. The object of such connecting surfaces—which by those skilled in the art usually are denominated “cross serrations”—is to lock the components of the tool also in the other co-ordinate direction. In such a way, turning of the cutting insert is counteracted. Examples of cutting tools featuring connecting surfaces having oblique or crossing engagement portions in the form of male- and female-like, respectively, engagement portions, are disclosed in, among others, U.S. Pat. No. 3,629,919, U.S. Pat. No. 5,810,518, U.S. Pat. No. 5,931,613 and U.S. Pat. No. 6,146,060.
Common to earlier known connecting surfaces of the type generally mentioned above, is that they include a comparatively great number of pairs of co-operating flanks, which should be brought into contact with each other when connection of two tool components is carried out. As a representative example of this, reference is made to the above-mentioned U.S. Pat. No. 5,931,613, which accounts for a cutting tool, the cutting insert and insert seat of which are formed with connecting surfaces, each one of which includes no less than five pairs of active, i.e., actively contactable, flanks. Clamping of the cutting insert in the insert seat of the basic body is carried out by means of a screw, which is inserted through a hole in the cutting insert, and is tightened in a threaded hole present in the basic body and mouthing in the insert seat. The tightening force that the screw applies to the cutting insert is accordingly applied in a reference locus, which is defined by the common, geometrical center axis of the screw and the holes. Of the five active flank pairs in the respective connecting surfaces, two are situated in front of the center axis, i.e., in an area between the same and an active, front edge of the cutting insert, while the other three flank pairs are situated behind the center axis. Of these rear flank pairs, two are mutually parallel and extend in a conceived extension of the two front flank pairs, while the third, rear flank pair is transverse, i.e., extends perpendicularly to the other flank pairs, the transverse flanks being spaced-apart and located on both sides of the center axis.
In theory, the connecting surfaces disclosed in the above-mentioned document offer a good solution to the problem of rigidly securing a cutting insert in an insert seat of a basic body. However, in practice, this solution—as well as similar solutions to the problem, which are based on the use of a greater number of force-carrying flank pairs—has turned out to be associated with drawbacks difficult to master. Thus, for a satisfactory function, it is required that all flanks not only in the connecting surface of the cutting insert, but also the connecting surface of the basic body, are manufactured with very narrow tolerances in order to guarantee such a good form and dimensional accuracy that the flanks in question de facto obtain force-transferring surface contact with each other. However, as soon as a smallest form defect unintentionally arises in any single flank, there is a risk that the cutting insert cannot be rigidly fixed in the insert seat of the basic body. In other words, the support of the cutting insert against the insert seat becomes over-determined, whereby the precision in respect of the position of the cutting edges in relation to the basic body is lost. In this connection, it should be borne in mind that individual cutting inserts, which constitute a mass produced wear part, never can be tailor-made for individual tools, in that the cutting insert is manufactured somewhere, usually from cemented carbide, while the basic bodies of the tools are manufactured elsewhere and from another material, usually steel.